In situ Study of the Long Term Sorption of Iodine onto Organic Matter
Iodine is generally present in environments as an anion (either iodide or iodate) and is therefore soluble in groundwater and migrates relatively quickly through rock and overburden to low-lying landscape positions such as wetlands where it can be retained by the organic matter of soils (iodine can only be retained in its oxidised form). This reaction with phenols, for example, is well known for I2 or I3-; the question is what controls the oxidation. Organic matter and bacterial activity seem to play an important role). Peat bogs are often located at low-lying landscape positions and are very rich in organic matter and therefore iodine is likely to "accumulate" in peat bogs.
An 18 month experimental study has been initiated, which aims to increase understanding of the mechanisms that govern the mobility and transport of iodine in peat bogs, and to acquire values for assessment models such as soil Kd and plant CR (concentration ratio). The study will focus on:
- the biogeochemical cycle of iodine in the peat bog including:
- the transfer of iodine along the carbon cycle in the peat bog (plant uptake, speciation of iodine in the plant, consequences of the biodegradation of the plant material on the availability of iodine in the peat); and, - the role of the redox potential on the migration and the speciation of iodine in the peat bog.
- the retention of iodine onto the peat; and
- the relation between the chemistry of organic matter and the retention of iodine.
Such an understanding of the mechanisms that govern the fate of iodine in peat bogs will form the basis for a better model of the transfers of this element in these types of ecosystems.